Heating, ventilation and/or air conditioning (“HVAC”) systems are common and indeed essential in most, if not all, modern buildings, structures and other human-occupied spaces. HVAC systems seek to maintain the indoor air quality (“IAQ”) at an acceptable level within such spaces by providing comfortable and healthy conditions in terms of air temperature, humidity, composition and cleanliness. HVAC systems constitute a significant part of a building's energy budget, particularly in extreme climates.
The heating, ventilating and air conditioning functions of HVAC systems cooperate to maintain thermal comfort, acceptable IAQ levels and pressure relationships between two or more human-occupied spaces within a building or other structure. HVAC systems, for example, may circulate air through the rooms of a building using an air handling unit, which mechanically forces air to flow through a network of ducts installed within the building, while adjusting air temperature and humidity to maintain comfortable conditions. While these typical HVAC systems have one or more air filters for capturing small particles and/or vapors, more thorough treatment is well-beyond the capability of these conventional filters. As a result, to maintain the IAQ of a building at an acceptable level, traditional HVAC systems exhaust some fraction of the contaminated indoor circulating air outside the building as exhaust air and replace it with some amount of fresh outside air, also known as “makeup air”. This process of changing or replacing indoor circulating air with makeup air is done primarily to counteract the accumulation of organic and inorganic contaminants created by human occupants, machines (e.g., computers or copiers), cleaning agents, building materials and/or pesticides, which gradually compromise the quality and safety of the indoor air. Removing such contaminants directly from the indoor air, rather than replacing the indoor air with makeup air from outside a building, may reduce the energy required to cool, dehumidify and/or heat makeup air or eliminate the need to use makeup air altogether.